Drive devices typified by robots mostly use a motor. However, general motors are heavy and have problems of occurrence of sounds, vibration, and electric noises. Thus, in fields of robots with high human compatibility, such as welfare robots and robots for rehabilitation, a demand for soft actuators that softly and strongly move like muscles instead of motors has being increased.
As former soft actuators, an IPMC actuator using an ionic conductive polymer (IPMC: Ionic Polymer Metal Composite), an SMA actuator using a shape memory alloy (SMA), a soft actuator utilizing electrochemical stretching of a conductive polymer, and the like have been developed.
In the IPMC actuator, when a voltage is applied to the ionic polymer metal composite containing an electrolyte, positive ions move to the negative pole side and, simultaneously therewith, a large amount of water having positive ions moves to the negative pole side in the polymer. As a result, the polymer swells at the negative pole side in which water has gathered with the positive ions. In contrast, at the positive pole side, the polymer contracts corresponding to the amount in which water has decreased. The polymer bends due to the phenomenon of swelling and contraction, which is used as the power for the actuator.
The IPMC actuator has advantages in that driving with a relatively low driving voltage (about 1.5 V) can be achieved, the responsiveness is high (0.1 second or lower), the durability is high (allowing 100,000 or more times of bending), the size can be easily reduced, the power consumption is low, and driving over a long period of time can be achieved. Thus, a large amount of research and development has been performed for the IPMC actuator at present (e.g., Patent Documents 1 to 3).
The SMA actuator utilizes, as an actuator, a phenomenon in which even when a shape memory alloy, in which a given shape is memorized beforehand, is deformed by applying a stress at a low temperature, the alloy recovers the shape memorized beforehand upon heating the same at a temperature higher than a certain temperature (e.g., Patent Documents 4 and 5). The SMA actuator has advantages in that the generative force is high and the structure of a high shrinkage structure is easy.
In the soft actuator utilizing electrochemical stretching of the conductive polymer, the chemical structure of the polymer or polymer structure changes due to an electrical oxidation-reduction reaction by applying electricity to the conductive polymer, whereby motions like muscles are developed in the polymer (Patent Documents 6 to 8). The soft actuator of this type has advantages in that the shape is easily maintained, the power conversion efficiency is high, driving with a voltage as low as 1.5 V or lower can be achieved, the size can be easily reduced, and the weight is light.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 6-6991
[Patent Document 2]
Japanese Unexamined Patent Application Publication No. 2007-267471
[Patent Document 3]
Japanese Unexamined Patent Application Publication No. 2007-318960
[Patent Document 4]
Japanese Unexamined Patent Application Publication No. 2007-247593
[Patent Document 5]
Japanese Unexamined Patent Application Publication No. 2007-138721
[Patent Document 6]
Japanese Unexamined Patent Application Publication No. 11-169393
[Patent Document 7]
Japanese Unexamined Patent Application Publication No. 11-169394
[Patent Document 8]
Japanese Unexamined Patent Application Publication No. 2006-299842